This page is intended as a brief overview of delimited continuations and related constructs, and how they can be used in Haskell. It uses the library CC-delcont as a vehicle for doing so, but the examples should be general enough so that if you have another implementation, they should be relatively straight forward to port (whenever possible, I have endeavored not to use the operators on abstract prompt and sub-continuation types from CC-delcont, instead using the more typical, functional operators).
Packages are available on Hackage:
The library is cabalized, so installation should be as simple as:
runhaskell Setup.lhs configure runhaskell Setup.lhs build sudo runhaskell Setup.lhs install
(to install to the default directory, /usr/local/lib on Unix)
4 More Information
A google search for delimited continuations will likely yield plenty of interesting resources on the subject. However, the following resources proved especially useful to the author when he was investigating them:
- Delimited continuations in operating systems -- This paper provides excellent insight into how delimited continuations can arise as a natural solution/model for real problems, specifically in the context of implementing an operating system.
- A Monadic Framework for Delimited Continuations -- This is the paper from which the implementation of the above library was derived. It's quite thorough in its explanation of the motivations for the interface, and also has several possible implementations thereof (though CC-delcont uses only one).
- Delimited Dynamic Binding -- This paper, and related code, served as the basis for the dynamically scoped variable portion of the CC-delcont library. It explains the rationale for having dynamic scoping and delimited control interact in the way they do in the library, and goes through the implementation of dynamic variables in terms of delimited continuations.
- Shift to control -- This paper explores four different sets of delimited control operators (all of which are implemented in CC-delcont), and their implementation. Though it's not directly relevant to this particular library, it provides some good insight into delimited continuations and their implementation in general.
- Oleg Kiselyov's continuation page -- Contains plenty of excellent information on delimited continuations and the like (including some of the above papers), including examples of their use in Haskell.